Microchannel plates may be used in various devices including light amplification devices to intensify an image where limited light is available, such as at night where an ordinary person would find the darkness impossible to penetrate with unaided eyes. Such aid is provided by light amplification devices which find application in security work, where police officers or security guards may use them for protection or to detect intruders, and in military applications, where soldiers use them for battlefield surveillance.
The microchannel plate comprises a bundle of very small cylindrical tubes which have been fused together into a parallel configuration. The plate is formed with parallel surfaces wherein each tube has a passageway between an opening onto the parallel surfaces. The inner surface of each passageway is coated with a high secondary emission material while the parallel plate surfaces are coated with a layer of electrically conductive material for placing a high electrostatic field between the plate surfaces.
When used in a light amplifier, a microchannel plate is placed between a photocathode and a target electrode. The light image focused upon the photocathode causes electrons to be emitted therefrom in proportion to the intensity of the light detected thereby. The electrons travelling from a particular location on the photocathode are directed by the electrostatic field to, and enter correspondingly located, passageways in the microchannel plate. As an electron enters a passageway, it strikes the side wall of the passageway which, due to the material coating thereon having a characteristically high coefficient of secondary emission, causes the re-mission of a number of electrons which again strike the inner surface of the passageway to re-emit a larger number of electrons and this effect continues down the channel length giving rise to a cascading increase in electrons. The increased number of electrons, hence amplified electron intensity, exit the individual passageways in the microchannel plate where, under the influence of another electrostatic field, they are accelerated toward a corresponding location on a target electrode, typically a phosphorus screen. This action is repeated at all other locations on the photocathode and microchannel plate to produce a visual image or mosaic representation of the original image upon the target electrode.
One problem with the microchannel plate is that those electrons not striking the inner passageway will strike the conductive, parallel surface of the multichannel plate and bounce back toward the photocathode or toward adjacent passageways. These electrons do not contribute to the signal but add to the noise factor.